Technical Field of the Invention
This invention relates generally to electro-mechanical conversion and more particularly to motors and/or gearboxes.
Description of Related Art
As is known, there are various types of electric motors and an almost endless variety of uses for them. For instances, an electric motor may be an AC motor (e.g., synchronous or induction), a servo motor, a DC motor, or an electrostatic motor (e.g., magnetic motor) and may be used in applications that range from micro-mechanical systems (MEMS), to food processing equipment, to household appliances, to power tools, to automobiles, to toys, to large manufacturing equipment, etc. Basically any device that uses mechanical motion includes an electric motor.
Due to the vast uses of electric motors, they come in an almost endless variety of sizes, shapes, and power levels. For instance, the size of a MEMS motor is small enough to fit on an integrated circuit and supplies nano-watts of power, while a large manufacturing equipment motor may be tens of feet in diameter supplying hundreds of thousands of kilowatts of power. Note that power of electric motors is sometimes expressed in horsepower, where one horsepower equals 746 watts.
Regardless of the type, size, shape, and power level, an electric motor includes a stator and a rotor. The stator or rotor includes coils that produce a magnetic field, which causes motion of the rotor (e.g., its shaft rotates). Typically, the speed at which the shaft rotates is not the desired speed of the device incorporating the motor. In these instances, the motor is coupled to a separate gearbox.
As is known, a gearbox provides a speed-torque conversion. For example, a gearbox may be used to slow the rotation down and increase the torque. As another example, a gearbox may be used to increase the speed of rotation and reduce the torque. In addition, a gearbox may be used to change the angle of rotation (e.g., a right-angle rotation).
When a motor and a gearbox are used in a food-processing device, they must be able to withstand constant washings with water and/or other cleaning agents. For these applications, the motor is contained in a watertight stainless steel housing and the gearbox is contained in its own watertight stainless steel housing to produce a “washdown” motor and a “washdown” gearbox. In addition, the motor must be able to continue to operate normally if some moisture does penetrate its watertight stainless steel housing.
Utilizing separate stainless steel housings, or shells, for a motor and a gearbox is expensive since most motor shells are manufactured from carbon steel and most gearbox shells are die cast aluminum, iron, or zinc. For example, a typical motor shell is fabricated from a steel plate that is rolled, welded, drawn over a mandrel (e.g., sized), and then painted. The resulting shell has an inside diameter that is slightly smaller than the stator laminations to provide a press fit of the AC stator. This process would be very expensive if used to manufacture a stainless steel housing. Similarly, using a die-casting method to create a stainless steel housing is very expensive. As such, using stainless steel housings requires new tooling, a new design approach, and/or a new manufacturing approach, which are less expensive.
While stainless steel is the preferred housing for a motor and a gearbox in food processing devices, a motor and gearbox may be contained in a common aluminum housing for non-food processing devices. These aluminum housed motor-gearboxes, however, are not designed to meet the “washdown” requirements of food processing devices and would quickly corrode and eventually fail if used in such devices.
Therefore, a need exists for a motor-gearbox assembly that can withstand the rigorous requirements of food processing devices and that can also be economically produced.